Optical instruments with reflective and refractive components such as coated mirrors and lenses are subject to contamination when used in space environments aboard the shuttle spacecraft, satellites and research rockets. Typical space experimental instruments operate in or near the vacuum ultraviolet wavelengths, and include a telescope, a spectrometer and photodetector with six or more optical surfaces.
A relatively small loss in reflectivity and transmission of each surface could result in either huge uncertainties in the data recovered or, even worse, the loss of meaningful data due to greatly reduced instrument sensitivity. Surface contamination of the optical components may result, even in the vacuum of space, from outgassing and subsequent deposition of hydrocarbons et al on the optical surfaces, bombardment by particles and chemical etching. Some of the surface contamination is reversible; a mirror may degrade when cold, then outgas volatile contaminants when heated by exposure to the sun; and generally, degradation is not linear with time so that measuring the efficiency of the surfaces at the beginning and at the end of a mission will not accurately determine the efficiency of the instrument at the time experimental data was taken.
It is the object of the present invention to provide spectrometric apparatus which will accompany experimental optical instruments on a space mission and measure the degradation of their optical components during their experiment.